Effects Of Ultrasound Treatment And Controlled Relative Humidity/Temperature On Straw Mushroom(Volvariella Volvacea)Postharvesting And Its Possible Mechanism

Straw mushroom?Volvariella volvacea Bull.Sing?is an edible fungus natively grown in tropical and subtropical regions of China.It has the delicious taste,tender meat and rich nutrition with high export amount.However,fresh fruit body of straw mushroom contains high moisture and crisp tissue which would result in the vulnerable mechanical damage.It also has a strong respiration and metabolic activity leading to the weightlessness,shrinkage and browning during postharvest process.Especially,straw mushroom belongs to the tropical/subtropical species which will suffer the chilling damage and fruit body autolysis under the conventional 0-4 ^oC condition,which affects the cold chain storage and the long-distance distribution.Therefore,researching and developing the postharvest preservation methods of straw mushrooms is an urgent issue.Currently,various methods including irradiation and chemical preservation with dehydroacetic acid have been proposed to prolong the straw mushrooms shelf life.However,it is still not reasonable to solve the problem of large quantities and long-term preservation of straw mushrooms due to the comlex operation procedures and chemical residues.As a non-thermal preservation technology,ultrasounds attracted the interests in Agaricus bisporus and fruits and vegetables preservation due to its easy operation and uninvolved chemical preservatives.Hence,the present study mainly aimed to investigate the effect of ultrasound treatment combined with temperature/humidity control on the postharvest quality and preservation period of straw mushroom,the activities and expression levels of the respiratory enzymes involved the respiration,and the structures and functions of mitochondria,and energy and respiration metabolisms,which would benefit for elucidating its possible mechanism.The main obtained results are as follows:?1?Effects of different ultrasound combined with temperature/humidity control on post-harvest quality of straw mushroom were investigated.The results showed that ultrasound treatment with 3,10,and 30 min delayed the changes in color and aroma of straw mushrooms,maintained a higher hardness,and kept a lower level of weight loss and MDA content.Under the optimal conditions?ultrasound treatment 10min,15^oC and 95%RH?,the fruit bodys after 4-d storage showed compact appearance and original aramo,the respiration rate were controlled 149.8 mgkg^-1h^-1,low weight loss rate of 28.83%and MDA content of 5.06 nmol/g.The soluble total sugar and protein also showed lower levels of 28.32 mg/g and 30.27 mg/g,respectively,with the lowest protease activity value of 35 U/g.The PPO activity and browning degree were 286.11Ug^-1 and 4.06,which indiacting that enzymatic browning reaction were significantly inhibited.?2?Effects of ultrasound treatment combined with temperature/humidity control on respiratory mechanism of straw mushroom were studied.Resuls showed that ultrasound treatment inactivated the activity of key enzymes?PGI,SDH,and CCO?of the respiratory metabolism of straw mushrooms.For example,on the 4th day of storage,the PGI activity decreased to 0.01 U·g^-1,the SDH activity decreased to 5.4U·mg^-1prot,the CCO activity decreased to 14.63 U·mg^-11 prot.The RT-qPCR results further confirmed that enzyme activity has a positive correlation with its gene transcriptional expression level.Moreover,ultrasound treatment moderately down ragulated the expression of vvPGI gene,vvSDH gene and vvCCO genes.?3?Effects of ultrasound treatment combined with temperature/humidity control on mitochondrial structure and function as well as energy metabolism of straw mushroom were studied.Results showed that the optimal postharvesting condition maintained the mitochondrial structural integrity and the compartmentalized structure,kept the uniform reticular structure of mycelium,delayed the disintegration rate of mycelium and alleviated the decline of the mitochondrial function of straw mushroom.At the 4th day of storage,the mitochondrial membrane fluidity was maintained at 81.8F·g^-1,the MPTP was kept at 0.53?A g^-1,inhibited the mitochondrial swelling rate,maintained a high mitochondrial membrane potential,and kept the H⁺-ATPase activity at 269.8 nmol Pi min^-1 mg^-1 prot,inhibited the decrease of ATP content?>66.51?g/g?and ADP content?>33.02?g/g?as well as the increase of AMP content?<49.18?g/g?,delayed the consumption of energy value?>0.56?.It shows that ultrasound treatment combined with temperature/humidity control can significantly reduce the decrease of mitochondrial function and delay the energy deficit during storage of straw mushroom.